EVOHs are excellent in transparency, and have excellent gas barrier properties (for example, oxygen barrier properties), aroma retaining properties, solvent resistance, oil resistance, mechanical strength and the like, and are typically formed into films, sheets, bottles and the like, which are widely used for various types of packaging materials such as food packaging materials, medical drug packaging materials, industrial chemical packaging materials and agricultural chemical packaging materials.
Such an EVOH can be produced by preparing an ethylene-vinyl ester copolymer through copolymerization of ethylene and a fatty acid vinyl ester such as vinyl acetate, and saponifying the ethylene-vinyl ester copolymer in an alcohol solvent such as methanol in the presence of an alkali catalyst under higher-temperature higher-pressure conditions.
It is possible to convert the EVOH alcohol solution prepared under the higher-temperature higher-pressure conditions through the saponification into an EVOH water/alcohol mixture solution stable at an ordinary pressure by replacing a part of the alcohol of the solution with water, then extrude the EVOH water/alcohol mixture solution in a coagulation bath mainly containing water at a lower temperature for solidification in the form of strands, cut the strands for pelletization, and dry the resulting pellets to provide a product.
In this EVOH preparation process, however, the alcohol is liable to run into the coagulation bath. The alcohol is evaporated in air, thereby impairing a working environment.
To solve this problem, there has been proposed a method in which most of the alcohol in the EVOH alcohol solution is replaced with water, and the resulting hydrous EVOH is supplied into an extruder and kneaded while being dewatered (see, for example, PLT1).
On the other hand, PVAs have excellent gas barrier properties (oxygen barrier properties), can be formed into films and sheets, and are widely used for various types of materials.
Such a PVA can be produced by preparing a polyvinyl ester through polymerization of a fatty acid vinyl ester and saponifying the polyvinyl ester in the presence of an alkali catalyst solvent such as methanol. A product of the PVA is provided by extruding the resulting PVA alcohol solution in a coagulation bath mainly containing water at a lower temperature for solidification in the form of strands, cutting the strands for pelletization, and drying the resulting pellets. Therefore, this PVA production process suffers from the same problem.